The present invention relates to irrigation systems and more particularly to irrigation systems wherein the irrigation fluid is directed to the irrigation sites by a plurality of irrigation tubings having the irrigation fluid emerging therefrom at a low volume flow rate.
So-called "drip" irrigation systems are not new in the irrigation art, but, because of severe drought conditions throughout portions of the United States in recent years, such systems have recently gained increased popularity. In such systems, rather than having large volumes of irrigation water spread from a single source over a large area whereby much of the water is lost due to run-off and evaporation, drip irrigation systems conduct the irrigation water directly to the base of the plants and the like being watered through a plurality of small diameter flexible tubes. The irrigation water emerges from the tubes at a very low pressure and flow rate so that the irrigation process is carried on for an extended period of time whereby the irrigation water is caused to penetrate deeply into the soil surrounding the roots immediately adjacent the plant.
In most such drip irrigation installations, the irrigation water is delivered to a location approximate the irrigation site by conventional metal or plastic water pipe containing the irrigation water under pressure. Some means must, therefore, be provided for accepting the high pressure irrigation water as an input thereto and providing an outlet for the attachment of a drip irrigation tube (the open end of which is placed at the base of the plant) and including internal means for dropping the pressure and the flow rate of the irrigation water being delivered to the drip irrigation tube at the output. Typically, the pressure dropping function is accomplished by passing the irrigation water through an orifice.
Taking an avocado or orange grove as an example, in a new grove only one or two application points for the delivery of drip irrigation water may be desired adjacent each tree. In a mature grove, up to six application points disposed radially around the trunk may be desired to provide an optimum watering pattern to the roots of the tree. In such an application, a delivery rate for the irrigation water of approximately two gallons per hour is desirable. The orifice employed in such apparatus is, of course, a function of the pressure in the irrigation water supply line. "Standard" line pressure in a watering system is 15 pounds per square inch (psi). At 15 pounds per square inch, a short orifice (e.g. a hole in a bulkhead or the like) of approximately 0.015 inch diameter is typically employed to provide the desired flow rate.
While such orifices work well under laboratory conditions or for a short while following initial installation, they are prone to clogging from debris flowing in the irrigation water and from eventual build-up of lime deposits and other minerals contained within the irrigation water. This is particularly true in the water available in many of the states of the southwestern region of the United States wherein such drip irrigation water systems are most desirable for use.
Numerous attempts have been made to solve the problem of the clogging of the small orifices in drip irrigation systems according to the prior art. For example, some orifices are made to be adjustable. That is, the orifice is closed down for operation and expanded to a larger size for cleaning. While such orifices are, therefore, cleanable, the mean time between failure from clogging is not changed since the orifice size during operation remains the same--that is, small.
Some orifices are made self-adjusting by having the orifice passage of greater length and partially contained within a compressible medium such as rubber disposed longitudinally to the flow path. Thus, as pressure builds up in the delivery line, the rubber or the like is compressed causing the orifice passageway to be reduced in size. While there is some degree of flexure attendant to such a design, it is typically not sufficient to maintain the orifice in a cleaned condition. Moreover, most of the deposits occur on the non-flexing portions of the rubber plug adjacent the orifice opening due to the stagant flow areas created thereby.
Another technique employed is the use of an extended helical (e.g. threaded) path. For example, the irrigation water may be passed through such a passageway of about 0.030 inch diameter for a distance of 36 inches to effect the desired pressure drop. The disadvantages of such an approach are self-evident.
In still another attempt at solving the problem, the water is passed through a series of orifices of about 0.025 inch diameter typically located in a rubber disc. Such an approach has one disadvantage in that increases in pressure tend to stretch the rubber and expand the orifices. This is, of course, just opposite of the desired reaction. Despite the shortcomings, this latter approach is the one presently favored in most commercial applications since the 0.025 inch orifice size is less prone to clogging than the 0.015 inch size while the rubber disc is an inexpensive and easily replaced item in contrast to the other more exotic apparatus available.
Additionally, prior art drip irrigation systems do not provide a workable means for adjusting the flow rates of individual groupings of irrigation tubes in a manner which affords the user thereof with reasonable control of the drip irrigation rates employed.
Wherefore, it is the object of the present invention to provide a cleanable sprinkler head for drip irrigation applications which is resistant to clogging and which provides the operator with a usable method of controlling the flow rates through individual clusters of irrigation tubes.
Moreover, it is a further objective of the present invention to provide drip irrigation apparatus providing the aforementioned objectives in a configuration particularly well-adapted for use in the easy conversion to a drip irrigation system of conventional high flow rate irrigation systems with existing buried underground supply piping having risers emanating therefrom.